Chain Architecture Dependence of Morphology and Water Transport in Poly(fluorene alkylene)-Based Anion-Exchange Membranes

Main-chain non-ether anion-exchange membranes (AEMs) have become a research hotspot in recent years because of their ease of preparation and excellent alkaline stability. However, owing to the limitations of the types of monomers and polymerization mechanisms, preparing main-chain non-ether AEMs with controllable morphology remains challenging. Herein, seven poly(fluorene alkylene) membranes, including random and block-structured membranes with different quaternary ammonium (QA) group distributions on the side chains, with the same ion-exchange capacity (IEC) were designed via superacid-catalyzed polymerization. The properties of the as-synthesized membranes were characterized, and the water-transport mechanism has been discussed in relation to the morphology of the membranes. The formed bicontinuous phase structure based on block biphenyl units possessed multidirectional ion channels and distinct ion clusters favorable to water molecule movement. The conductivity of the optimized membrane with a block biphenyl structure reached 208 mS cm-1 at 80 degrees C, and the peak power density of an H2/O2 fuel cell based on the as-prepared membrane was 0.92 W cm-2. The reported approach is effective in balancing the content of free and bound water within the membrane, generating maximum hydroxide mobility and water transport suitable for high-performance AEM fuel cells. This study highlights the significance of regulating the block structure and adjusting the segment distribution in AEMs to tune their morphologies and provides an innovative design approach for constructing high-performance AEMs.

Automated summary

Main-chain non-ether anion-exchange membranes (AEMs) have gained significant attention due to their ease of preparation and excellent alkaline stability. However, the controllable morphology of these membranes remains challenging. In this study, seven poly(fluorene alkylene) membranes with different quaternary ammonium (QA) group distributions were designed via superacid-catalyzed polymerization. The morphology of the membranes was found to play a key role in water transport and ion conductivity. The optimized membrane with a block biphenyl structure exhibited high conductivity and peak power density, making it suitable for high-performance AEM fuel cells.